I just posted my first question on here the other day about installing vapor barriors in crawspaces… appriciate all the responces!
This same house has no insulation at all in the cs, so the next part of that job I am trying to convince the homeowner to take is to insulate the parameter of the crawspace. The best solution I can come up with is to install 2×6’s 16oc around the inside parameter of concrete block, and stuff R19 in between.
The vapor barrior I put down on the ground extends about 1 foot up the 3 foot wall and is glued to the wall, so the insulation would overlap the vapor barrior at the bottom.
I was planning to use non-faced insulation, since I have been told the kraft paper facing the open area would be a fire hazard.
As far as opening up forced air ventalation to the cs, I figured tapping into the duct work under the house with 1 or 2 vents, then putting in the same number of vent registers though the floor to make a path back to the return.
Does anyone know of a better way to do this?
Replies
Is the crawlspace presently vented? How dry is it down there? What area do you live in; ie what is the climate like there?
It's dry now in the cs now that I have installed the wall to wall completly silled vapor barrior, but there are puddles of condensation everywere underneth it.
I'm located in Raleigh, NC so we have a moderate climate - hot as hell in the summer, cold as crap in the winter.
The house does have vents all around the parameter of the cs to the outside, just as all the rest of the houses around here do.
I was proposing to the homeowner that since the vents can let in warm moist air in the summer, causing condensation under the house, that we close them up permenantly and then heat and cool the crawspace. It dosn't seem to be the conventional way it's done around here, but after reading that artical in FHB, it seemed to make alot of sense.
st
I live in Raleigh too. Advanced Energy is a company that is based here too and administers the federally funded home building part of the Energy Star program for the area. They promote sealed crawl spaces, but in their own literature, it says that sealed crawl spaces roughly double the incidence and concentration of radon in the homes living space (on average - not every case). Not something I'd like to be responsible for. Also, if you want to close off the vents you need to find a way to water proof them so that the batt insulation you propose to cover them with doesn't get wet. Also, if you want to frame the walls with 2x6 up against the crawl space block walls, the wood would need to be PT. Although the new PT wood is supposed to be safer, you would still have PT lumber inside the living space in the sealed crawl space configuration you are proposing. Sealed crawl spaces are more typically insulated with rigid foam, but then you get into problems with the foam being a possible fire hazard. Also, by having insulation (of any type) on the walls, you are creating an easy path for termites to get up to the home's wood floor system. Another thought is that you will need to convert the crawl space door into something that is more air tight and possibly insulated.
You are probably thinking that I have not provided you with any answers, just more questions, but I guess what I'm trying to say is that I wouldn't try to convince a customer to change over to a sealed crawl space - at this point there are too many questions. Building science has shown that crawl space venting is probably not effective for moisture control, but IMO, the brain boys haven't given us a great, workable alternative either. I have thought seriously about trying it on my house, but I'd be monitoring the situation, and it would take a few years to decide if it was a sucess or failure...
If you still want to pursue it there was a great article in JLC about sealed crawl spaces about a year ago, and it was even based on recommendations of a NC contractor. This guy has had some inspection problems with respect to the foam & fire code thing though...
Really though, you haven't said why you feel it is necessary to convert to a sealed crawl space... Is there a moisture proble down there? A moisture probe used on the floor framing is a good place to start. Matt
Edited 11/14/2004 1:34 pm ET by DIRISHINME
I would say that you're about done... On the inside... Insulating the perimeter wall will have no real effect unless there is a significant temp differential across the wall. You won't have the differential unless you introduce heated/cooled air into the space. I feel that the potential harm of the insulating outweighs the benefits. I also think the cost of heating/cooling the space outweighs the benefits. (My apologies the author in FHB a few months ago who advocated doing this. I just don't think the costs can be justified on a retrofit.)
Assuming there are no other immediate problems, the most I would do is maybe a ventialtion fan and/or a dehumidifier. If the homeowner wants to spend a bunch of money, go forth with insulation and HVAC modifications.
The moisture accumulating under the vapor barrier probably needs to be attacked from outside. Better drainage outside of the building. After the exterior issues are solved, might you actually need to go in and remove part of the barrier to allow the soil/air under it to dry. With all of that done, you would have a CS fit for a king.
I'm in Durham, so I can relate to the climate. We have had some very wet weather this year, and no real drought for several years. CS moisture is probably about as bad now as it will ever normally get.
I leave my CS vents open at all times except when there is a threat of freezing the pipes. I have my HVAC ducts running in the CS (ducts are steel and uninsulated). In times of severe cold, I depend on the heat loss through the ducts to keep the CS above freezing. (I also have no insulation in floor joist space, so I have I am also heating the CS through the floor.) This is certainly not the most efficient from a utility standpoint, but it avoids a lot of other issues. I can also get away with this because I never use A/C. A/C in our climate will cause massive sweating of the uninsulated ductwork. I would never advocate running A/C in uninsulated ducts in this climate.
I would not install a HVAC vent in the sealed CS unless you are really condient that the air in there is clean. Either by a return duct (which you suggest) or by pressure differential (the cheap and not very intelligent way), CS air will be mixing with living space air. The return duct would work, but I want the mother of all filters on it before it gets back the air handler.
Not an expert... Just a lifelong DIY resident of the RDU area.
the logic in my mind about going to a sealed crawspace was that the air down there was already breathing up through the floor anyway. The ducts are allready leaking air into the space, and since they dont' allready have insulation, put it up on the parameter and seal it off. Doesn't seam like it would cost extra to heat the area down there, contrary, it should save some energy with the insulation.
As for the blocking, I was planning to use whitewood, instead of treated. Using L brackets to stand it off the block 1/2 inch, not touching the ground nor the top. But the insulation would be from the plastic to the subfloor.
you made some interesting points about radon and such. Nothings ever simple is it? Maybe the time honored method of insulation up between the floor joist is best for now.
Do you remember the title of that JLC artical, or post a link to it. I looked around the site, but couldn't find it.
thanks
st